Molecular Beam Epitaxy

At CMU, the research group of Prof. Feenstra in collaboration with
Prof. Greve of the Electrical and Computer Engineering Department
has developed a molecular beam epitaxy (MBE) system for the growth
of GaN films. Studies will focus on the atomic-scale structures formed
during growth on SiC, including the initial stage of heteroepitaxy,
strain relaxation, and development of thick GaN films.
This project began in Jan, 1996, and as of Nov, 1996 the
MBE system
system was fully assembled and growth experiments were underway.

The system consists of two parts: an L-shaped analysis chamber
with 10 inch diameter, and a spherical growth chamber with
14 inch diameter. The
growth chamber
uses solid sources for Al, Ga, Mg, and Si deposition,
and a gaseous rf-plasma source for N atoms.

Two separate types of sample mounting schemes have been used. In the first,
resistive heating of SiC substrates will be used. This will enable
STM imaging on hot substrates, and, in principle, operation of the
STM inside the growth chamber during deposition of the GaN.
The second scheme uses more conventional moly-blocks with bayonet-type
mounts. The sample blocks are held on a
manipulator
with
integral heater
during the growth. Two-axis rotation is possible with the manipulator,
to allow sample transfer and also for reflection high-energy electron
diffraction (RHEED) characterization during the growth.

The
tunneling microscope
is in-house designed and constructed. It employs a
double-stage spring suspension system.
The coarse approach mechanism for the STM is constructed using Inchworm
piezoelectric motors (Burleigh Corp.). Also, the piezoelectric tube scanner
and tip mounting apparatus is obtained from Park Scientific, and will
function in both a tunneling mode and a force mode, with the latter using
the piezoresistive cantilevers for measuring tip deflection.